1. Technical Field of Invention
The present invention relates, generally, to power regulation systems and, in particular, to providing precisely regulated power to a microelectronic device such as a microprocessor. Precision power regulation is accomplished by accurate lossless current measurements, temperature compensation and digital calibration.
2. Background of the Invention
Regulated power supplies or voltage regulators are typically required to provide the voltage and current supply to microelectronic devices. The regulator is designed to deliver power from a primary source to an electrical load at the specified current, voltage, and power efficiency. Switching power converters (SPC) also referred to as Buck regulators are commonly used voltage regulators due to their high efficiency, high current capability, and topology flexibility. In addition, they can be designed to provide very precise voltage and current characteristics required by devices such as microprocessors, microcontrollers, memory devices, and the like.
Power requirements for emerging leading edge technology microprocessors have become very difficult to satisfy. As the speed and integration of microprocessors increases, the demands on the power regulation system increase. In particular, as gate counts increase, the power regulation current demand increases, the operating voltage decreases and transient events (e.g. relatively large voltage spikes or droops at the load) typically increase in both magnitude and frequency. Some emerging microprocessors are expected to run on less than 1.3 volts and more than 100 amperes.
SPC's utilizing step-down multi-phase Buck converters have been the preferred topology to meet the low voltage and high current requirements of microprocessors. With the advent of increasingly complex power regulation topologies, digital techniques for power converter control, specifically in multiphase designs, can improve precision and reduce the system's total parts count while also supporting multiple applications in the same power system through digitally programmable feedback control.
Existing feedback controls have taken voltage measurements from the load, as well as from the individual output phases. The feedback information has been used to adjust the width of the pulses produced by each of the phases of a multi-phase buck regulator system to bring the supplied voltage and current within the load line tolerances specified by the microprocessor manufacturer. Active Transient Response (ATR) has been used for high frequency response to rapidly changing power requirements at the load by quickly activating multiple phases to supply or drain (as the case required) more current to or from the load, thereby temporarily over riding the generally slower overall voltage regulator system response.
The measurement of load current is important for meeting microprocessor power requirements that specify a load line and active voltage positioning by defining narrow parameters within which current must be supplied at a specified voltage. In addition, leading edge microprocessors may specify current levels that must not be exceeded to avoid damage. Nevertheless, realization of accurately measured current amplitude has been problematic.
One way of measuring load current would be to insert a precision resistor in the load current path. For example, the precision resistor can be inserted In series with the inductor to measure current through each phase of the high side FETs. As another example, a precision resistor can be connected between the low side FET and ground. The voltage across the precision resistor divided by the known value of the resistor provides the amplitude of the current. This technique is lossy as the precision resistor consumes power and generates heat. This heat generation and power loss is a substantial problem that is even more significant when operating under battery power.
The power loss can be reduced by inserting a resistor and taking a current measurement in only one phase and extrapolating that measurement to approximate the current in the other phases. However, this reduces the accuracy of the measurements and fails to provide information for balancing the channels. Moreover, the power that is consumed and the heat that is generated by this lossy technique is still excessive and undesirable.